Over 1,000,000 Americans suffer from severe visual disturbance because of retinal and choroidal diseases. Unfortunately, neither a means of cure nor prevention exists for most of these diseases. The primary obstacle to further progress is the lack of sufficient understanding of the fundamental processes of the retina and choroid. Some biochemical interactions between cells must occur in the interstitial fluid. Therefore, analysis of interstitial fluid may yield important information concerning the functional and metabolic states of cells and their environment. Subretinal fluid represents the in vivo microenvironment of the photoreceptor cells, Muller cells and pigment epithelium. As such, the subretinal fluid should contain the chemical components involved in the biochemical exchange between the neuroretina and the retinal epithelium, including intermediates of the visual pigment metabolism. Choroidal fluid represents, in part, the biochemical exchange of nutrients and waste products between the choroidal blood supply and the subretinal fluid. Therefore, study of these interstitial fluids should yield important information concerning the biochemistry and physiology, including the pathochemistry and/or pathophysiology, of the retina and choroid. The overall objective of this research is, first, to provide critically needed information concerning the normal biochemical and cytological activities in the subretinal space and choroidal space; second, to study the pathochemistry of the hereditary retinal degenerations in rats and dogs; third, to study the possible pathochemical mechanisms of the photic retinopathies in rats; and fourth, to study the mechanism of retinal transfer between the sensory retina and the retinal epithelium. Electrophoresis, high pressure liquid chromatography and electron microscopy are the methods of choice. In conclusion of this research we will be able to provide normal criterion and possible pathochemical and pathocytological mechanisms of some retinal and choroidal diseases.